public static IList <IList <int> > PalindromePairs(string[] words)
{
TrNode root = new TrNode('^');
var ans = new List <IList <int> >();
for (int i = 0; i < words.Length; i++)
{
Build(root, words[i], i);
}
for (int i = 0; i < words.Length; i++)
{
List <int> result = new List <int>();
Search(root, words[i], result);
foreach (int ids in result)
{
if (ids == i)
{
continue;
}
List <int> pair = new List <int>();
pair.Add(i);
pair.Add(ids);
ans.Add(pair);
}
}
return(ans);
}
private static void CheckPalindrumForMiddleChars(TrNode node, String str, List <int> result)
{
if (node.end && IsPalindrome(str))
{
result.Add(node.index);
}
foreach (var child in node.children)
{
CheckPalindrumForMiddleChars(child.Value, str + child.Key, result);
}
}
private static void Search(TrNode node, String str, List <int> result)
{
if (str.Length == 0)
{
CheckPalindrumForMiddleChars(node, "", result);
return;
}
if (node.end && IsPalindrome(str))
{
result.Add(node.index);
}
char c = str[0];
if (node.children.ContainsKey(c))
{
Search(node.children[c], str.Substring(1, str.Length - 1), result);
}
}
private static void Build(TrNode node, String str, int index)
{
int len = str.Length;
if (len == 0)
{
node.end = true;
node.index = index;
return;
}
char ch = str[len - 1];
if (!node.children.ContainsKey(ch))
{
node.children.Add(ch, new TrNode(ch));
}
Build(node.children[ch], str.Substring(0, len - 1), index);
}
//https://www.youtube.com/watch?v=-vdScGc8ebI&t=322s
public static string[] join_words_to_make_a_palindrome(string[] words)
{
TrNode root = new TrNode('^');
bool flag = false;
var ans = new List <IList <int> >();
for (int i = 0; i < words.Length; i++)
{
Build(root, words[i], i);
}
for (int i = 0; i < words.Length; i++)
{
List <int> result = new List <int>();
Search(root, words[i], result);
foreach (int ids in result)
{
if (ids == i)
{
continue;
}
List <int> pair = new List <int>();
pair.Add(i);
pair.Add(ids);
ans.Add(pair);
}
if (ans.Count > 0)
{
flag = true;
break;
}
}
if (flag == true)
{
return(new string[] { words[ans[0][0]], words[ans[0][1]] });
}
return(new string[] { "NOTFOUND", "DNUOFTON" });
}
